1. Field of the Invention
The present invention relates to adhesive compositions for surgical use. More particularly, it relates to novel compositions, which are adjusted to have a suitable viscosity and a reduced cytotoxicity. The novel compositions have a softness similar to the soft tissue of a living organism and are easily biodegraded and bioabsorbed into the living organism at a moderate speed after healing. These novel compositions result from improving .alpha.-cyanoacrylate adhesive composition.
2. Description of the Related Art
Suturing and anastomosis of a wound is one of the most important operating techniques in any surgical operation. Therefore, the healing speed of the wound makes most of the difference between a good or a poor operation. Nowadays, the material compositions and operating methods for improving the speed of healing are continuously improving. For example, there have been improvements in methods for suturing a wound, and many good sutures have become readily available as a result. However, special techniques are still necessary in operations involving microvascular anastomosis and nerve sutures. Therefore, new inventions concerning adhesive methods for use in the living body system are needed to shorten surgical operations. There are many proposed reports and inventions all over the world for the above purpose.
The .alpha.-cyanoacrylate adhesive compositions are already widely sold in the market as adhesive compositions for surgical use. However, they remain of limited use in special clinical applications, because they often leak due to the low viscosity of the composition. The leakage sometimes damages the soft tissue. Additionally, these adhesive composition have a high cytotoxicity for the living cell.
The inventors of this patent have already disclosed several means (JP. Pat. 116409/1995) to remedy the above defects. This patent concerns new compositions for surgical use, in which a homo-polymer of lactic acid (DL-, D- and L- type), a co-polymer of lactic acid and glycolic acid or a co-polymer of lactic acid and .epsilon.-caprolactone are added to the .alpha.-cyanoacrylate adhesive composition as a thickening agent and a stabilizer. The resulting composition is easily biodegradable and bioabsorbable into the body of the living organism.
However, this patent fails to disclose the cytotoxicity of the surgical adhesive composition for the living cell, and, therefore, the cytotoxicity for the living cell is still uncertain. Weight-average molecular weights of the homo-polymer of DL-lactic acid and the co-polymer of lactic acid and .epsilon.-caprolactone are about 140,000 and 220,000 respectively, which is a relatively high molecular weight, so they are suitable as a thickening agent. The patent also fails to disclose the effects of molecular weight on plasticizing after hardening, and the hydrolyzing velocity of co-polymer compositions of lactic acid and .epsilon.-caprolactone when employed as a thickening agent.